The modulation of O-phosphotyrosyl-utilizing signal transduction processes is being addressed through the development of site-directed inhibitors of protein-tyrosine kinases (PTKs). Two approaches are being pursued: In the first approach hydroxylated aryl analogues are being prepared which are intended to inhibit the binding of tyrosyl-containing substrate within the catalytic site. Included among these are a series of bicyclic compounds designed as conformationally constrained styryls as well as non-amine containing analogues of the potent natural product PTK inhibitor, lavendustin A. Inhibitor testing has been conducted in the following PTK systems: epidermal growth factor receptor (EGFR); p56lck; lyn; c-erb B 2/HER 2/neu. High potency and interkinase specificity have been observed for some members of the series. Work is continuing in whole cell systems. In the second approach, phosphonomethyl phenylalanine (Pmp) as well as monofluoro-Pmp (FPmp) and difluoro-Pmp (F2Pmp) derivatives have been prepared and incorporated into peptides as phosphatase resistant and hydrolytically stable mimetics of O-phosphotyrosyl residues. Replacement of the O-phosphotyrosyl residue (Y*) in the peptide "GY*VPML" with F2Pmp gave "G[F2Pmp]VPML", which was equally able to inhibit the src homology region 2 "SH2"-mediated association of the p85 subunit of phosphoinositol-3 (PI3) kinase. Additional linear peptides as well as the cyclic analogue, "cyclo(G[F2Pmp]VPML)" were also effective inhibitors. Efforts are currently in progress to prepare peptidomimetics based on these peptides, which have the ability to inhibit specific SH2-interactions.